Question Unlocking Shop Help

So I'm making a KitPvP plugin with purchasable kits via money in vault.
And I don't know how to make a unlocking system. So when you click the kit you will get the perm and your money will get decreased by how much you spent on it. And when you click it again you will be able to use it with out it spending your money. And it doesn't matter if you have to do it in another GUI.
Thank you!